Such X-ray tubes are generally known for example in the form of microfocus X ray-tubes and are used for example to examine printed circuit boards in the electronics industry. The known X-ray tubes include a target which is struck by high-energy-accelerated electrons or other electrically charged particles when the X-ray tube is operating, with the result that X-radiation is produced in generally known manner. The thus-produced X-radiation is used in imaging methods in order for example to represent components or component arrays on printed circuit boards and in this way visually examine the printed circuit boards.
X-ray tubes of the type concerned in the form of microfocus X-ray tubes are known for example through DE 102 51 635 A1 and DE 103 52 334 A1. They include a target and means of directing an electron beam at the target. In such X-ray tubes, the target usually consists of a base body which serves as a mechanical support and also to dissipate electric charges and heat. A layer, provided as a retarding layer, of a target material, in which the striking electrons are slowed, is arranged on the support. The target material is chosen in such a way that, when the electrons strike and are slowed, X-radiation results in a desired wavelength range.
When the high-energy-accelerated electrons strike, only approximately 1% of the energy of the electrons is transformed into X-radiation, while the remaining approximately 99% are transformed into heat. In this way the target is exposed to a strong thermal load stress and subjected to relatively high wear. The wear occurring in this way at the target can lead to a reduction in the quality of the X-ray images produced by means of the X-ray tube, or malfunctions may occur in the X-ray tube. In the case of a deterioration in image quality or of malfunctions, fault diagnosis is time-consuming, and thus costly, in the case of the known tubes. In order to establish whether a malfunction has occurred because, for example, the target is worn away, the casing of the X-ray tube must be opened and the target visually examined This is particularly time-consuming and thus costly.